EP0710686A2 - Polyols and process for their preparation from PET-waste or waste from the PET-production - Google Patents

Abstract

The prodn. of polyols in the form of bifunctional aromatic polyester-alcohols (I) from scrap PET or PET prodn. waste comprises (a) dissolving the waste material in diethylene glycol (DEG) in amts. such that the polyester-alcohol obtd. after trans-esterification has an OH no. of >700 mg KOH/g, (b) trans-esterification in the presence of suitable known catalysts, after removing any undissolved solid if necessary, with distn. of at least some of the liberated ethylene glycol (EG), and (c) removal of free DEG by distn. of the equilibrium mixt. obtd. at <140 degrees C, to give a polyester-alcohol with an OH no. of 260-500. Also claimed is a storable polyol with an OH no. of 260-500 as above, with a content of higher oligomers which is lower than the equilibrium content for the OH no. of the prod..

Description

The invention relates to polyols in the form of bifunctional aromatic polyester alcohols which have a combination of a relatively low hydroxyl number (OHZ) and a relatively low molecular weight oligomer fraction, and to a process for their production from waste from polyethylene terephthalate (PET) or from waste from PET production.

Aromatic polyester alcohols are valuable substances which are widely used in industry, preferably as part of the so-called A component for the production of rigid polyurethane foam. They increase the flame resistance and stiffness of the foam. There are various processes for the production of these valuable compounds, in which primary raw materials are used exclusively or partially as starting materials.

In processes for the production of bifunctional aromatic polyester alcohols, in which only primary raw materials are used as starting materials, the acid component used is essentially phthalic anhydride (anhydride of orthophthalic acid) in conjunction with diethylene glycol (DEG) as the dihydric alcoholic component.

Various proposals are known from the literature to use terephthalic acid from polyethylene terephalate wastes as an acid component for the production of polyols. These processes are based on the glycolysis of Polyester waste and transesterification with DEG.
The physical behavior of the terephthalic acid / polyester alcohols produced by these processes differs from polyester alcohols based on orthophthalic acid, in particular with regard to their storage stability. For example, from the initially liquid terephthalic acid polyester alcohols, produced by glycolysis and transesterification of PET waste with DEG, provided that they have a range of hydroxyl number (OHZ) that is suitable for further processing, solids increasingly separate after a few days of storage, which eventually cause the product to transition to a slushy consistency.

To circumvent this disadvantage, a number of processes for the production of polyester alcohols have been proposed, in which, in addition to terephthalic acid based on PET waste, other aromatic or aliphatic dicarboxylic acids are used. For example, documents US-A-4608432, US-A-4546169 and EP-A-0152915 describe polyol mixtures made from phthalic anhydride, PET waste and DEG. In the documents US-A-4439550, EP-A-0248570 and DE-C-3435014, in addition to phthalic anhydride, adipic acid, glutaric acid, succinic acid and isophthalic acid are proposed as sole or combined additional components. The molar proportion of such additional dicarboxylic acids is generally 50% and more, based on the total acid content.

In a further proposal to obtain storage-stable terephthalic acid polyester alcohols, it is proposed to use glycols with a higher molar mass in addition to DEG for the glycolysis and transesterification process. US-A-4444919 describes a PET glycolysate based on DEG and triethylene glycol. US-A-4469824 proposes the use of a mixture of DEG and dipropylene glycol.

Processes that combine both methods have also become known.

For example, USP 4720571 provides for a mixture of PET waste and DMT production residues (mixture of predominantly methyl esters of iso-, ortho- and terephthalic acid) to be reacted with at least two higher glycols.

All these proposals have the serious disadvantage that valuable and costly primary raw materials must be used in addition to the PET waste. When using aliphatic dicarboxylic acids or glycols with a higher molecular weight than DEG there is a further disadvantage of a reduction in the aromatic content in the polyol and thus a reduction in the positive effects resulting from the use of aromatic polyester alcohols, e.g. in polyurethane production.

It is known that polyester alcohols are not a uniform product in terms of their molecular weight. In the same way as for the high-polymer polyesters, the molecular weights are subject to a distribution that has been mathematically formulated by Schulz and Flory. From this functional relationship it is deduced that the equilibrium is continuously shifted with increasing OHZ in favor of the content of free DEG and at the expense of the content of higher oligomers.
In the specific case, this means that in the curve of the molecular weight distribution of a polyester alcohol based on terephthalic acid and DEG, for example with an OHN of 315 mg KOH / g, the maximum is at the monomeric diester, with about 14% by weight of free DEG and one with increasing degree of polymerization decreasing proportion of oligomers up to degree of polymerization 10 is present in the equilibrium mixture. Such a product is not stable in storage.

Only those glycolysates that have an OH of more than 700 mg KOH / g have proven to be stable in storage. However, polyols with such a high OHZ are unsuitable for reaction with diisocyanates due to the existing equivalence relationships.

The object of the present invention is to provide polyols in the form of aromatic To provide polyester alcohols in which the acid component consists essentially of terephthalic acid from PET waste or PET production waste and the diol component consists essentially of DEG and which, despite this composition, has good storage stability.

According to the invention, this object is achieved by a process which enables the production of polyester alcohols which differ in their molecular weight distribution substantially from the products obtained in previously known processes. While known products - as explained above - have a molecular weight distribution due to the equilibrium reaction, which is determined entirely or approximately by the position of the chemical equilibrium, which corresponds to the OHZ set in each case, the products according to the invention contain a considerably lower proportion of higher molecular weight oligomers.

• die Abfälle in Diethylenglykol gelöst werden, wobei das Mengenverhältnis von Abfällen zu Diethylenglykol so gewählt wird, daß der nach der anschließenden Umesterung erhaltene Polyesteralkohol eine Hydroxylzahl größer 700 mg KOH/g aufweist,
• die in DEG gelösten und erforderlichen- oder gewünschtenfalls von Feststoffen befreiten Abfälle unter Einsatz bekannter Umesterungskatalysatoren umgeestert werden, wobei das hierbei freigesetzte Ethylenglykol zumindest teilweise abdestilliert wird,
• und daß aus dem im Gleichgewicht befindlichen Umesterungsprodukt bei einer Temperatur von unter l40 °C freies DEG so weit abdestilliert wird, daß ein Polyesteralkohol mit einer OHZ von 260 - 500 mg KOH/g erhalten wird.

The present invention thus relates to a process for the production of polyols in the form of bifunctional aromatic polyester alcohols from PET waste and waste from PET production, which is characterized in that

• the wastes are dissolved in diethylene glycol, the quantitative ratio of wastes to diethylene glycol being chosen so that the polyester alcohol obtained after the subsequent transesterification has a hydroxyl number greater than 700 mg KOH / g,
• the wastes dissolved and, if necessary or freed from solids, dissolved in DEG are transesterified using known transesterification catalysts, the ethylene glycol released in this process being at least partially distilled off,
• and that free DEG is distilled off from the transesterification product in equilibrium at a temperature below 140 ° C. to such an extent that a polyester alcohol with an OHN of 260-500 mg KOH / g is obtained.

The process according to the invention is based on the surprising finding that the equilibrium which occurs at higher hydroxyl numbers, for example at an OHN of> 700 mg KOH / g, is maintained with regard to the ratio between monomeric diester and oligomers when the free DEG is at a temperature of below 140 ° C, preferably of max. 130 ° C, separated by distillation and thus the OHZ is reduced to the desired value. The removal of the DEG at this temperature is possible according to the invention if the process is carried out at a pressure of less than 2 hPa, preferably less than 1 hPa. In this way, polyester alcohols are obtained which, depending on the completeness of the DEG separation, can be specifically adjusted to OHZ values of 260-500 mg KOH / g. The products obtained show no separation of solids even after prolonged storage.

With the help of HPLC using tetrahydrofuran / water as eluent, the changes in the molar mass distribution that occurred were visibly demonstrated. While the distribution curve for an OHZ product in equilibrium reached 315 mg KOH / g up to oligomers with a degree of polymerization (P _n ) of 10, for the product according to the invention it practically falls to zero, at least for oligomers with a degree of polymerization of more than 6 but on extremely low values. The resulting proportion of oligomers with a degree of polymerization above 6, based on the total proportion of oligomers, for the polyols according to the invention should generally be below 1% by weight, preferably below 0.5% by weight.

The chromatograms of the HPLC analysis of a typical polyol according to the invention and a conventionally produced polyol of the same OHZ give, for example, the values for the oligomer fractions, based on the total fraction of the oligomers (ie without monomeric diesters), which can be seen from the following comparison: Olgomer fractions, based on total oligomer fractions. Degree of polymerization P _{n of} the oligomer Conventionally made polyol Polyol according to the invention P _n = 6 5.6% by weight 0.9% by weight P _n > 6 7.0% by weight undetectable

If the product according to the invention is heated again, an increase in the DEG content and thus a gradual resetting of the equilibrium applicable to the OHZ is found at temperatures above 140 ° C. At a temperature of 230 ° C, the full equilibrium is restored within a short time. The product properties then correspond to those of a terephthalic acid polyester alcohol produced by known processes.

The process according to the invention is carried out in such a way that the waste is first dissolved in a reactor which is advantageously provided with a stirring device under normal pressure and nitrogen blanketing. Temperatures up to 250 ° C are appropriate for high polymer material, temperatures up to 205 ° C are sufficient for low molecular weight distillation residues. The amount of DEG is to be measured so that after the later transesterification process an OHZ of greater than 700 mg KOH / g is reliably achieved. For this, depending on the equipment conditions, a molar ratio of PET (based on the molecular unit mass of 192 g / mol) to DEG of 1: 5 to 1:10, preferably 1: 6.6 to 8.0, is required.

It can be advantageous to carry out the dissolving process only with part of the necessary amount of DEG and to add the rest only immediately before the transesterification stage. This applies in particular to distillation residues of PET production which fluctuate greatly in composition, where the required residual amount of DEG can only be determined by determining the saponification number and the terephthalic acid content derived therefrom after the dissolving process.

If necessary and desired, the wastes are filtered after complete dissolution, the filtration conditions depending on the degree of contamination. With waste containing TiO₂ and distillation residues, the use of special filter media is necessary to achieve a clear filtrate. A mixture of equal parts of cellulose chips, crystalline microcellulose and purified diatomaceous earth has proven useful as a filter layer.

The ethylene glycol (EG) is then released from the filtrate in a glycolysis and transesterification process and separated by distillation. The extensive removal of the EG is advisable in order to obtain products of low viscosity and to reliably avoid the separation of solids. An EG content of max. 10%, advantageously of max. 5 in the final product. Known catalysts, for example tetrabutyl titanate, cobalt acetate, manganese acetate or zinc oxide, are to be used for the rapid course of the transesterification process.

The glycolysis and transesterification process can be carried out, for example, in a heatable stirred reactor which is equipped with a distillation column. The column should have a sufficient separating action in order to keep the DEG content in the distilling EG as low as possible. A partial vacuum is required for the process control, the height of which is also determined by the flow resistance of the column and is expediently to be set such that in the last phase of the transesterification process a product temperature of over 210 ° C, preferably over 225 ° C, for example 230-235 ° C is achieved. Chromatographic investigations have shown that the proportion of oligomers is reduced to the equilibrium state within a technically advantageous reaction time only at this temperature. Depending on the equipment conditions, the pressure required for this can be in the range of 500 - 750 hPa.

After completion of the EG separation, the reactor contents are cooled to below 140 ° C. and, bypassing the column, the DEG is distilled off at a residual pressure of, for example, 1 hPa and a product temperature of below 140 ° C., preferably a maximum of 130 ° C., until the required OHZ for the product has been reached. This can optionally be in a range between 260-500 mg KOH / g. The product is then discharged.

The method according to the invention can be used for PET waste, for example from bottles, foils, tapes, film material and fibers, and for waste from PET production, for example distillation residues from vapor preparation, casting waste, residues from chip dedusting and faulty batches. It has the advantage of greater economy because, apart from the waste material as raw material, only DEG, which is a by-product of EC production and a cheap diol, is used.
Another advantage of the process according to the invention is the lower viscosity of the polyester alcohols produced thereafter compared to polyester alcohols of the same OHZ, which were prepared by known processes.

Another object of this invention is the storable polyol which can be prepared by the process according to the invention described above in the form of a bifunctional aromatic polyester alcohol.
This product according to the invention is characterized in that its OHZ is within a range of 260-500 mg KOH / g and it contains a proportion of higher oligomers which is lower than the equilibrium proportion which corresponds to the respective OHZ.
Preferred polyols according to the invention are those which, based on the total oligomer content, contain not more than 1% by weight, preferably not more than 0.5% by weight, of oligomers with a degree of polymerization greater than 6, in particular those which are practically free are of oligomers with a degree of polymerization greater than 6.
Furthermore, those storable polyols according to the invention are preferred whose Free and bound EG content max. Is 10% by weight.

The polyols according to the invention are suitable for all technical applications in which the use of polyols with a relatively low OHZ, which have a very low proportion of higher molecular weight oligomers, is necessary or desirable, preferably for example as a component of the A component in the production of polyurethanes, in particular of polyurethane foams. The following exemplary embodiments illustrate particularly advantageous embodiments of the method according to the invention.

example 1

1000 g PET bottle waste was dissolved in a 6 l reaction vessel in 3700 g DEG at a temperature up to 240 ° C with stirring and nitrogen blanketing. After the dissolution process was complete, the product was cooled to 180 ° C. and separated from the impurities contained as solids by filtration through a suction filter lined with filter paper.

The filtrate was transferred to a likewise heated 6 liter stirred reactor with an attached column and, after adding 200 mg of tetrabutyl titanate, heated at a pressure of 680 hPa. The column was equipped with 10 bubble trays and a heated outer jacket. After reaching a temperature of 225 ° C in connection with the full glycolysis and transesterification process, the distillation of EG began. By setting the column jacket temperature to 186 ° C and regulating the top temperature by varying the reflux ratio to 186 ° C, the distilling EG could be largely separated from DEG. The product temperature increased with the amount of EG distilled off and was 235 ° C. at the end of the process with a top temperature dropped to 175 ° C. The transesterification product had an OHN of 728 mg KOH / g.

The product was then cooled to 130 ° C and gradually Increasing the vacuum distilled the free DEG bypassing the column. The pressure at the end of the distillation process was 0.2 hPa, the temperature of the product 130 ° C.

1770 g of light yellow polyol with an acid number of 0.9 mg KOH / g, an OHN of 325 mg KOH / g and a viscosity at 25 ° C. of 2100 mPa · s were obtained. No solids separated from the product during storage.

Example 2

1808 g of distillation residues from the vapor preparation in PET production were dissolved in a 6 l reaction vessel in the same amount of DEG at a temperature of 205 ° C. with stirring and nitrogen blanketing. The strongly cloudy solution was then cooled to 180 ° C. and filtered through a suction filter with a filter layer, consisting of a mixture of 25 g pulp chips, crystalline microcellulose and purified diatomaceous earth.

The clear filtrate obtained in an amount of 3597 g had a saponification number of 228.5 mg KOH / g, corresponding to a terephthalic acid content of 33.9%. To achieve the desired OHN of greater than 700 mg KOH / g after the transesterification process was complete, 2795 g of DEG were added to the filtrate, taking into account the amount of DEG already contained in the distillation residues, and 360 mg of tetrabutyl titanate as the transesterification catalyst.

The mixture was treated further as in Example 1, the transesterification product having an OHN of 709 mg KOH / g.

2274 g of light brown polyol with an acid number of 1.1 mg KOH / g, an OHN of 305 mg KOH / g and a viscosity at 25 ° C. of 3500 mPa · s were obtained. No solids separated from the product during storage.

Claims (13)

Process for the production of polyols in the form of bifunctional aromatic polyester alcohols from PET waste and waste from PET production, characterized in that the wastes are dissolved in diethylene glycol (DEG), the quantity ratio of wastes to DEG being chosen so that the polyester alcohol obtained after the subsequent transesterification has a hydroxyl number (OHZ) greater than 700 mg KOH / g, the wastes dissolved in DEG and, if necessary or freed from solids, are transesterified using known transesterification catalysts, the ethylene glycol (EG) released in this process being at least partially distilled off, - And that free DEG is distilled off from the transesterification product in equilibrium at a temperature below 140 ° C. to such an extent that a polyester alcohol with an OHN of 260-500 mg KOH / g is obtained. Process according to Claim 1, characterized in that the waste is dissolved in DEG at a minimum temperature of 200-250 ° C which is dependent on the degree of polymerization of the waste. Method according to at least one of claims 1 and 2, characterized in that the dissolving process takes place only with a partial amount of the required DEG portion and the remaining amount is added after analytical characterization of the product before the transesterification process. Method according to at least one of claims 1 to 3, characterized in that the waste dissolved in DEG for the separation of solids contained in the form of suspended matter or suspensions are filtered if necessary using filter media. Process according to at least one of Claims 1 to 3, characterized in that during the transesterification the EG is distilled off to such an extent that the end product has a content of max. 10% by weight, preferably of max. 5 wt .-% EG in free and bound form. Process according to at least one of Claims 1 to 5, characterized in that the transesterification is carried out at a pressure of 500-700 hPa and a product temperature of up to a maximum of 235 ° C. Process according to at least one of Claims 1 to 6, characterized in that free DEG from the transesterification product in equilibrium at a temperature of max. l30 ° C is distilled off. A storable polyol in the form of a bifunctional aromatic polyester alcohol according to claim 1, characterized in that its OHZ is within a range of 260-500 mg KOH / g, and it contains a proportion of higher oligomers compared to the equilibrium proportion which corresponds to the respective OHZ , is reduced. A storable polyol according to claim 8, characterized in that it contains, based on the total oligomer content, not more than 1% by weight, preferably not more than 0.5% by weight, of oligomers with a degree of polymerization greater than 6. A storable polyol according to at least one of claims 8 and 9, characterized in that it is practically free of oligomers with a degree of polymerization greater than 6. A storable polyol according to at least one of claims 8 to 10, characterized in that its free and bound EG content contains max. Is 10% by weight. A storable polyol which can be prepared by the process of claim 1. Use of the polyol of claim 8 in the production of polyurethanes, in particular polyurethane foams.